# SaltyRover Chassis — BOM + Assembly Notes
**Rev A — 2026-03-01 — sl-mechanical**
**Issue: #73**

---

## Overview

SaltyRover is the stable 4-wheel variant of SaltyLab.
Low CG, wide track — designed not to tip over.
Reuses the 25 mm vertical stem, sensor head, RPLIDAR, RealSense,
IMX219 camera mounts, and roll cage from SaltyLab without modification.

```
Top view (schematic):

          Forward (+Y)
               │
   ◉─────────────────────◉   ← front axle (AXLE_BASE/2 = 170 mm forward)
   │     [Orin NX]       │
   │     [battery]       │   ← flat packs below deck (low CG)
   │     [battery]       │
   │       [FC]          │
   ◉─────────────────────◉   ← rear  axle
           │
       stem (centre)

Dimensions (approx):
   Robot width (tyre-to-tyre):  ~810 mm  (TRACK_W=540 + 2×TIRE_W/2)
   Robot length (axle-to-axle): ~340 mm  (AXLE_BASE)
   Deck width:                   480 mm
   Deck length:                  500 mm
   Ground clearance:             ~50 mm  (deck bottom to ground)
   Overall height (with 550 mm stem + sensor head): ~800 mm
```

---

## Height Stack

```
Z from ground:
  Z =   0 mm  — ground
  Z =  50 mm  — chassis bottom (battery tray floor)
  Z = 109 mm  — deck bottom face
  Z = 117 mm  — deck top face  (Z=0 in SCAD coords)
  Z = 127 mm  — motor axle CL  (+10 mm above deck top)
  Z = 139 mm  — deck stem collar top  (117+22)
  Z = 145 mm  — stem adapter flange top (139+6)
  Z = 173 mm  — stem clamp top  (145+28)
  Z = 723 mm  — stem top with 550 mm rover stem
```

---

## File Index

| File | Description | RENDER |
|------|-------------|--------|
| `saltyrover_chassis.scad` | Main deck plate, stem collar, standoffs | `assembly` / `deck` / `deck_2d` |
| `rover_motor_mount.scad` | L-bracket + axle clamp plate, 4× | `assembly` / `bracket` / `clamp_plate` / `bracket_2d` |
| `rover_battery_tray.scad` | Slide-out battery tray, 2–4 packs | `assembly` / `tray` / `rail` / `latch` / `tray_2d` |
| `rover_stem_adapter.scad` | Flange + split clamp, locks stem to deck | `assembly` / `base_flange` / `clamp_front` / `clamp_rear` |

---

## Part A — Deck Plate (`saltyrover_chassis.scad`)

### Structural parts

| # | RENDER | Qty | Material | Process | Notes |
|---|--------|-----|----------|---------|-------|
| 1 | `deck_2d` | 1 | 8 mm 5052-H32 Al | Waterjet or CNC router | 480×500 mm blank |
| — | — | — | **or** 8 mm PETG FDM | Print in sections, bolted lap joints | Prototype only |

### Fasteners (deck to motor brackets)

| # | Spec | Qty | Use |
|---|------|-----|-----|
| 2 | M5×20 SHCS | 16 | Motor bracket flange to deck (4 per corner × 4) |
| 3 | M5 hex nut | 16 | Captured on deck underside |
| 4 | M4×16 SHCS | 4 | Stem adapter flange to deck collar |
| 5 | M4 flat washer | 4 | Under bolt head |

---

## Part B — Motor Brackets (`rover_motor_mount.scad`)

Print or CNC 4×.  Each bracket handles one drive motor.

### Printed parts

| # | RENDER | Qty | Material | Settings | Notes |
|---|--------|-----|----------|----------|-------|
| 6 | `bracket` | 4 | PETG or PC | 5 perims, 60% infill | Print flange face down; add M5 inserts or use nuts |
| 7 | `clamp_plate` | 4 | PETG | 4 perims, 40% infill | Axle retention; print flat |

**CNC alternative:** `bracket_2d` → DXF, CNC route from 10 mm 6061-T6 Al plate.

### Fasteners

| # | Spec | Qty | Use |
|---|------|-----|-----|
| 8 | M4×20 SHCS | 8 | Axle clamp plate to bracket (2 per motor × 4) |
| 9 | M4 hex nut | 8 | Captured in bracket |
| 10 | Axle lock nut | 4 | Axle tip retention — **verify axle thread before ordering** (BOM.md: Ø≈10 mm tip) |
| 11 | M5×20 SHCS | 16 | Bracket flange to deck (from item 2 above) |

> ⚠ **Axle note:** BOM.md caliper values: base OD 16.11 mm, D-cut OD 15.95 mm, flat chord 13.00 mm.
> Verify AXLE_D / AXLE_FLAT / BEARING_OD in `rover_motor_mount.scad` before printing.

---

## Part C — Battery Tray (`rover_battery_tray.scad`)

### Printed parts

| # | RENDER | Qty | Material | Settings | Notes |
|---|--------|-----|----------|----------|-------|
| 12 | `tray` | 1 | PETG | 4 perims, 30% infill | Print open-top face up; no supports |
| 13 | `rail` | 2 | PETG | 5 perims, 40% infill | T-slot slide rail; print top-face down |
| 14 | `latch` | 1 | PETG or TPU 95A | 4 perims, 30% infill | Spring retention clip; TPU gives better snap feel |

### Fasteners

| # | Spec | Qty | Use |
|---|------|-----|-----|
| 15 | M4×12 FHCS | 6 | Slide rail to deck underside (3 per rail, countersunk) |
| 16 | M4 T-nut or nyloc | 6 | Captured under deck for rail bolts |
| 17 | M3×10 SHCS | 2 | Spring latch to tray end |
| 18 | Velcro strap 25 mm × 500 mm | 4–8 | Battery pack retention (1–2 per pack through tray floor slots) |

### Batteries

| # | Part | Qty | Spec |
|---|------|-----|------|
| 19 | Battery pack | 2–4 | 24 V, **420×88×56 mm** (BOM.md caliper-verified) |
| 20 | BMS board | 1 | Matched to cell chemistry; mount to deck underside near Y+ wall |

---

## Part D — Stem Adapter (`rover_stem_adapter.scad`)

| # | RENDER | Qty | Material | Settings | Notes |
|---|--------|-----|----------|----------|-------|
| 21 | `base_flange` | 1 | PETG | 5 perims, 40% infill | Print flat; add M4 brass inserts or use through-bolts |
| 22 | `clamp_front` | 1 | PETG | 5 perims, 40% infill | Flat-face down |
| 23 | `clamp_rear` | 1 | PETG | 5 perims, 40% infill | Mirror; flat-face down |

### Fasteners

| # | Spec | Qty | Use |
|---|------|-----|-----|
| 24 | M4×20 SHCS | 2 | Stem clamp clamping bolts |
| 25 | M4 hex nut | 2 | Captured in clamp rear half |
| 26 | M4×8 set screw | 1 | Rotation lock (front half) |
| 27 | M4×16 FHCS | 4 | Flange to deck collar (countersunk) |

### Stem tube

| # | Part | Qty | Spec | Notes |
|---|------|-----|------|-------|
| 28 | Vertical stem | 1 | 25 mm OD × 1.5 mm wall 6061-T6 Al, **550 mm length** | Cut from 1 m stock; SaltyLab uses 1000 mm |

> Sensor head, RPLIDAR, cameras, and roll cage from SaltyLab mount
> directly onto this 25 mm stem — no modifications required.

---

## Motors

Same hoverboard hub motors as SaltyLab.  **4× required for rover.**

| # | Part | Qty | Spec |
|---|------|-----|------|
| 29 | Hub motor | 4 | 10×2.125" tire, 36V nominal, ~350W; axle OD 16.11mm (caliper) |
| 30 | Motor cable extension | 4 | 6-pin JST-PH 300 mm hall sensor + 3-phase power |

---

## Mass Estimate

| Assembly | Est. mass |
|----------|-----------|
| Al deck plate | ~1.4 kg |
| Motor brackets × 4 (PETG) | ~0.5 kg |
| Hub motors × 4 | ~7.2 kg |
| Battery packs × 2 | ~1.4 kg |
| Battery tray (PETG) | ~0.3 kg |
| Stem + sensor head (from SaltyLab) | ~1.5 kg |
| Electronics (FC + Orin + wiring) | ~0.6 kg |
| Stem adapter + hardware | ~0.2 kg |
| Fasteners | ~0.3 kg |
| **Total estimate** | **~13.4 kg** |

> Wide 540 mm track + low 117 mm deck height → tip-over angle > 45°.
> CG is at approximately Z = 200 mm with packs flat and full payload.

---

## Assembly Sequence

1. **Deck plate:** Cut or print `deck_2d`.  Waterjet preferred for Al.
2. **Motor brackets:** Print (or CNC) 4× `bracket` + 4× `clamp_plate`.
   - Test-fit axle D-cut bore before assembling to deck.
3. **Slide rails:** Print 2× `rail`.  Bolt to deck underside.
4. **Stem adapter:** Print `base_flange` + `clamp_front` + `clamp_rear`.
   - Insert stem through deck collar bore; seat flange on collar top.
   - Bolt flange with 4× M4×16 FHCS.
   - Slide clamp halves on stem above flange; tighten M4 clamping bolts (1.5 N·m).
   - Tighten M4 set screw.
5. **Motor brackets:** Slide flange into deck edge slot; 4× M5×20 bolts.
   - Do not torque until axle alignment is confirmed.
6. **Motors:** Drop axle into bracket dropout slot.  Install clamp plate.
   - Tighten clamp M4 bolts.  Axle lock nut finger-tight + ¼ turn.
7. **Battery tray:** Slide tray in from +X with packs loaded.
   - Latch snaps at full insertion.
8. **Sensor head + stem accessories:** Install from SaltyLab as-is.
   - Recommend 550 mm stem for rover (sensor head at ~720 mm, stable).

---

## Tools Required

- M3/M4/M5 hex drivers
- Torque wrench: M5 structural bolts 4 N·m, M4 clamp bolts 1.5 N·m
- Thread locker (Loctite 243 blue) on axle lock nuts and stem clamp set screw
- Dial caliper — verify axle dimensions before bracket print/CNC